Non-impact electrographic printers generally use a dielectric surface to receive an electrostatic charge to form a latent image of the information that is desired to be printed; that latent image is, in accordance with known techniques, developed with a suitable toner and transferred to paper on which the image is thereafter fixed, as by heat. The electrostatic surface on which the latent image is formed is most often a moving dielectric surface on which electrostatic information is provided by a print head, and such a general combination can be found in U.S. Pat. No. 4,638,339 entitled "Electrographic Charge Deposition Apparatus" and assigned to the assignee of the present invention.
It is customary for non-impact printers to rely upon a recirculating charge receiving surface to carry the desired image through the various parts of the printing process. Laser and other optical printers generally use a photo sensitive material as the charge receiving surface whereas charge deposition systems need to cooperate with a dielectric material such as the surface of a rotating drum which has been coated with the necessary dielectric material. However, such a drum technique includes a surface that is subjected to wear and therefore replacement and, because such drums are precisely machined elements, the cost of replacing such drums can add significantly to the per sheet cost of the printed material.
An additional prior art technique is the use of a thin flexible belt of an appropriate material to carry the working dielectric surface through the system. However, the motion of the belt is exceedingly difficult to control and the belt transport system often becomes even more complex and expensive than the drum system. Attempts have been made to combine the belt and drum system by wrapping a belt around the outside of the drum and attempts have been made to correct the belt path problems by mounting the belt between elements such as bars and chains to overcome any belt forces which tend to cause the belt to go off track. Clearly avoiding any interrupted print cycle technique or discontinuous paper motion that results from using a discontinuous belt is to be desired but the provision of complex corrective belt tracking systems must be avoided to maintain the desired low cost in the cost per sheet printed.